A direct injection engine is provided with a variable valve timing mechanism, an exhaust gas recirculation (EGR) system and the like in order to improve output, reduce exhaust emission, and improve fuel economy. It is necessary to adapt a valve timing and an EGR ratio as well as a fuel injection timing and an ignition timing. Hence, control parameters to be adapted increases and an adaptation operation becomes complicated.
JP-2002-206456A shows that an engine characteristic is measured at predetermined measure points, a model is obtained which defines a relationship between control parameters and the engine characteristic, and adaptation values of the control parameters are computed by use of the model.
JP-2004-263680A shows that design of experiments method is used to reduce the number of measure points with high adaptation accuracy.
Since the number of control parameter to be adapted increases in the direct injection engine, even if the design of experiments method is used, the number of measure point increases to ensure the accuracy of the model. The adaptation operation is still complicated.
In the conventional method, since a combination of the adaptation parameter is difficult to obtain a normal combustion, the combination of the improper adaptation parameter may be included in the measure points arranged with the design of experiments method. As a result, abnormal combustion occurs with the improper combination of the adaptation parameter at the time of adaptation operations, and there is a possibility that the engine is damaged or the engine characteristic changed to deteriorate the model accuracy.
The present invention is made in view of the above matters, it is an object of the present invention to provide fuel-injection-timing adapting method and apparatus for a direct injection engine, which is capable of adapting the fuel injection timing accurately with adaptation operations reduced.
According to the present invention, an engine characteristic data is repeatedly measured by changing a fuel injection timing at a plurality of measure points which are arranged in a predetermined measuring range in order to compute an adaptation value of the fuel injection timing based on measure data at each measure point. A relationship between a behavior of a fuel spray injected into a cylinder through a fuel injector and a fuel injection timing is simulated based on design data of the engine and the fuel injector, and the measuring range of the fuel injection timing is refined based on a simulation result.
A fuel-spray behavior of the fuel injected into the cylinder through the fuel injector 13 is a major factor to obtain a stable combustion state. A computer simulates a relationship between the fuel-spray behavior and the fuel injection timing based on design data of the engine and the fuel injector. Based on the simulation result, a range where the combustion state deteriorates is excluded from the measuring range of fuel injection timing, and the measuring range of fuel injection timing is refined to the range in which the combustion state becomes stable. Hence, the fuel injection timing is effectively adapted.